Optical sensors for sensing the presence of an object within the viewing (sensing) field of an optical detector by monitoring reflected radiation, commonly light, from either a target behind the object or from the object itself have been known for many years. Such sensors are particularly commonly used as counters in applications where the object passes across the detector's viewing field and either reflects light incident thereupon towards the detector or interrupts a light beam incident upon a reflector. The source of the radiation is generally adapted by prisms and the like to provide a beam of radiation that enters the detector's viewing field at an angle that enables the radiation to be reflected from the object or the reflector, as the case may be, towards the detector. Conversely, the radiation source may be positioned opposite the detector to direct a beam of radiation directly at the detector rather than by reflection which if intersected by an object passing therebetween is able to act as a counter or perform some other function.
An example of photoelectric sensor heads used for such purpose is disclosed in pages 1-3 of Eaton Corporation's Publication No. 17203 which is incorporated herein by reference. Generally such sensors are particularly adapted to provide counting information by detecting the absence of light (intersection by an object in the sensor's viewing field) or the presence of light (reflection by an object in the sensor's viewing field).
Of interest to the present invention is the reflective type of sensor system in which the photoelectric sensor or optical detector receives radiation, commonly light, reflected from the object within the viewing field of the detector. The terms such as light, optical, photoelectric, viewing field, and the like as used herein are intended to encompass both visible and invisible radiant energy or radiation such as luminous and ultraviolet or infrared and other radiation as is apparent from the above Publication No. 17203.
Heretofore, it has been common practice to use a single beam of radiation for intersecting the detector's viewing field at an angle enabling it to be reflected towards and be received by the detector from an object present in a single zone defined within the boundaries of intersection between the detector's viewing field and the radiation beam. Generally, the effectiveness of the detector is influenced by the distance of the zone from the detector and the intensity of the radiation beam. However, the distance of the object from the detector may vary for particular applications. In order to change the location of the zone with respect to the detector to accommodate for particular distances of the object from the detector, it has heretofore been required to physically change the position of the radiation source so as to change the angle at which the radiation beam intersects the detector's viewing field and accordingly change the location of the zone within the detector's viewing field. Such practice is inconvenient and may often be difficult to accomplish resulting in a need to provide a more convenient and accurate means of enabling effective receipt by an optical detector of reflected radiation from an object over a broader distance range within the viewing field of the detector.